Process for the separation and purification of organic acids



0a. 17, 1939. H. Howm' 2,176,343

PROCESS FOR THE SEPARATION AND PURIFICATION 01 ORGANIC ACIDS Filed April 5, 1937 INVENTOR ffienry C.]fowd.rd

fl/lr Arte/"n eys Patented Oct. 17, 1939 PATENT QFFHC PROCESS FOR THE SEEARATION AND TPURI- FIGATIQN 3F ORGANIC ACIDS Henry C. Howard, Pittsburgh, Pa., assignor to Carnegie Institute of Technology, Pittsburgh, Pa., a corporation of Pennsylvania Application April 5, 1937, Serial No. 135,038

3 (Claims. (Cl. 204-9) This invention relates to a process for the separation and purification of organic acids. It can be applied to those water-soluble organic acids which form salts which are soluble in water 5 and those organic acids which form salts which are relatively insoluble in water. It is particularly useful for the separation and purification of organic acids obtained by the oxidation of coal, coke and other carbonaceous materials.

[0 The recovery of water-soluble organic acids in the fine state from their salts in good yields presents great difliculties. The usual procedure consists in double decomposition of a barium salt of the acid with sulphuric acid or a lead salt of the acid with hydrogen sulphide, removal of the precipitated "barium sulphate or lead sulphide by filtration, and recovery of the acid by evaporation of the filtrate. In such a procedure, the organic acid recovered is always contamilg nated with inorganic salts and must be purified by other means. Furthermore, there is the undesired byproduct of barium sulphate or lead sulphide. I have found that if a solution of the salts of u the water-soluble orga: .c acids obtained, for

example, by the oxidation of coil, coke or other carbonaceous materials, is placed in the central compartment of a three-compartment diaphragm cell, the diaphragms being composed of parchn ment or Cellophane for example, and electrolyzed with an insoluble anode, as for example, a platinum gauze, and a suitable cathode, as for example, a copper sheet or a copper tube through which water can be circulated for cooling; the organic acid can be recovered in a pure form in good yield by evaporation of the anode liquors and that the hydroxide of the metal of the orig inal salt can be similarly recovered by evaporation of the cathode liquors.

In the drawing, there is conventionally illus trated a three-compartment diaphragm cell suitable for carrying out my invention. The apparatus consists of a vessel Hl'formed from non-conducting material such as porcelain. The vessel 5 is divided into three fluid-tight compartments,

including end compartments A and C and a middle compartment B, by two partitions II and I2 of porous'membrane such as parchment or Cellophane. In the end compartment A, herein called the anodic" compartment, 9. suitable anode l3 formed from insoluble material, for example, platinum gauze, is located. In the end compartment C, herein called the cathodic"v compartment, a suitable cathode I4 formed, for example,

i from copper, is placed. The cathode is preferably hollow and has connected to the hollow portlon two pipes l5 and 16 by means of which a stream of cooling water can be circulated through the cathode. In many instances, it will be sufiicient if the cathode is made from an ordinary copper plate. The anode and the cathode have suitable connections to a source 01' direct current electricity. Under some circumstances, it may be desirable to cool the liquid in the anodic compartment while the process is being carried to out. Such cooling can be accomplished by placing a suitable cooling coil in the anodic compartment and causing a cooling fluid to be circulated therethrough. The coil should be made from a material such as glass which would not be lit attacked by or affect the anodic liquid.

In practicing my invention, the organic acid salt in water solution is placed in the middle compartment B and the anodic compartment A and the cathodic compartment C are filled with ac distilled water. The anode l3 and the cathode I are connected to a suitable source of direct current, not shown. The organic acid will pass into the anodlc compartment A through membrane II and the metallic hydroxide will pass as into the cathodic compartment 0 through the membrane l2. From time to time, depending upon conditions, it is advisable to draw off the liquors wholly 'or partly from the end compartments and to refill the compartments with 80 distilled water. The liquors collectedfrom the anodic compartment are then evaporated to obtain the organic acid; likewise, the liquors obtained from the cathodic compartment are evaporated to obtain the metallic hydroxide. 35

The method has been applied to the recovery of acids formed by the oxidation of coal. The chief oxidation products of bituminous coal are carbonic, oxalic, acetic, and aromatic acids, the distribution of the carbon of the original coal 0 in these acids being, respectively, approximately as follows: 48.5%, 15.9%, 2.3% and 33.3%. By electrolysis of a solution of, for example, the potassium salts of these acids, such as is obtained in an alkaline permanganate oxidation of 45 cool, it has been found possible to recover 86% of the oxalic acid and 96% of the aromatic acids ment and the continuous migration into and withdrawal from the end compartments of mellitic acid and ammonium hydroxide results in quantitative decomposition of the salt :and recovery of pure mellitic acid in solution in the anodic compartment, and of ammonium hydroxide in solution in the cathodic compartment.

The acid can be recovered from the anodic solution by evaporation.

My invention discloses a simple, satisfactory and economical process for the recovery of water-soluble organic acids from their salts.

I claim:

1. A process for the separation and purification or the aromatic-organic acids formed by the oxidation of coal, coke and carbonaceous substances which contain at least one six-membered 2. A process for the separation and purification of the aromatic organic acids formed by the oxidation of coal, coke and carbonaceous substances which contain at least one six-membered carbon ring with other carbon atoms attached thereto, by means of a three-compartment diaphragm cell having a middle compartment and an anodic, compartment having an insoluble anode therein and a. cathodic compartment, which consists in placing a solution of an alkaline metal salt of an acid in the middle compartment, placing distilled water in the anodic and cathodic compartments and passing direct current electricity through the cell, whereby the organic acid is caused to enter the anodic compartment and the metal of the salt is caused to enter the cathodic compartment on the opposite side-of the middle compartment.

3. A process for the separation and purification of the aromatic organic acids formed by the oxidation oi coal, coke and carbonaceous substances which contain at least one six-membered carbon ring with other carbon atoms attached thereto, by means of a' three-compartment diaphragm cell having a middle compartment and an anodic compartment having a platinum anode therein and a cathodic compartment having a water-cooled copper cathode therein, which consists in placing a solution of an'alkaline metal salt of the acid in the middle compartment, placing distilled water in the anodic and the cathodic compartments and passing direct current electricity through the cell, whereby the organic acid is caused to enter the anodic compartment and the metal of the salt is caused to enter the cathodic compartment on the opposite side of the middle compartment.

HENRY C. HOWARD. 

